1. Field of the Invention
The present invention relates to an adaptive array antenna controller.
2. Description of the Related Art
Transmission signals in mobile communication system are transmitted in a multipath transmission environment. In order to demodulate received signals well, it is necessary to appropriately process a variety of signals coming through several transmission paths. With respect to this point, the OFDM (Orthogonal Frequency Division Multiplexing) method is a promising technology in this technical field. In this method, data are carried on a plurality of carriers that have orthogonal relations with each other, and received signals are Fourier transformed and demodulated to provide a fade-proof communication system. This method is provided with a certain length of guard interval at each symbol, and therefore some delay signals can be limited within the guard intervals so as not to disturb the orthogonal relationship.
Ideally, all the delay signals arriving after delays from the leading wave (the first incoming wave) should be limited within the guard intervals. However some delayed signals (some path components) arrive over the guard intervals depending on the communications environment. Such signals with large delays form interference disturbing the orthogonal relationship between sub-channels, and prevent the recovery of transmitted signals. Accordingly, it is necessary to suppress such delayed signals by using adaptive equalizing techniques or adaptive array antenna techniques.
Conventional technologies for suppressing undesired delayed signals are described in “OFDM Adaptive Array for suppressing Doppler Shift”, Nishikawa, Yoshitaha Hara, Shinsuke Hara, The Institute of Electronics, Information and Communication Engineering, Technical Report A-P2000-90, October 2000; “Equalizer Training Algorithms for Multi-carrier Modulation Systems” J. S. Chow, J. M. Cioffi, and J. A. C. Bingham, International Conference on Communications, pp. 761-765, 1993; and “Asymmetric Digital Subscriber Line”, ITU-T Recommendation G. 992.1, 1999.
In these conventional technologies, each received and weighted signal from each of a plurality of antenna elements is converted into a digital signal, and each thus obtained digital signal is supplied to a digital processing part to adaptively adjust weighting coefficients of the antenna elements. In this method, plural digital signals each obtained from one of the adaptive array antenna elements are utilized and very accurate adaptive controlling is attained.
However, the conventional method needs to form a plurality of digital received signals based on the plurality of antenna elements. Therefore, a number of analog-to-digital converters corresponding to antenna elements are needed, the circuit is complex, and there are additional disadvantages regarding consumption of power, circuit size and cost, which are much more disadvantageous especially for small radios or mobile phones.